Power-driven toothbrushes are generally well-known. Through the use of various driving mechanisms, the bristles vibrate, oscillate or rotate so as to remove dental plaque thoroughly and quickly. The abrasion of gum tissue by use of excessive force (brush action), however, has been recognized to be a possible risk of power toothbrushes, and accordingly, many current power toothbrushes are designed to minimize abrasion of gum tissue as much as possible.
In addition to the use of such a toothbrush to remove dental plaque, power toothbrushes have been designed which produce an acoustical cleaning effect, which increases general performance as well as cleaning the subgingival area of the teeth between the teeth and gums and demobilizing the motile bacteria therein. The acoustic phenomenon is achieved by streaming/cavitation of fluid in the mouth, either saliva or other fluid. Examples of patents which teach a toothbrush producing the acoustic effect through sufficient bristle vibration include U.S. Pat. Nos. 3,924,335 and 3,809,977 to Balamuth, and U.S. Pat. No. 4,787,847 to Martin. Adequate cavitation to produce an acoustic effect requires a minimum instantaneous pressure change in the cavitational fluid in the mouth, which in turn requires a minimum instantaneous velocity of the bristles.
Numerous drive system designs for such a toothbrush have been designed. One example is shown in U.S. Pat. Nos. 3,535,218 and 3,676,218 to Sawyer, which utilizes a cantilevered beam arrangement with a fixed displacement driving mechanism, i.e. a motor crank and actuator arrangement. The beam is designed to operate as a spring element, but is positioned between the driver and the load, resulting in high source impedance and poor resistance to damping. In U.S. Pat. No. 4,175,299 by Teague, et al, an orbital brush arrangement is shown, using a lever which operates through a pivot which in turn converts the drive on one end of the lever to orbital action on the other end of the lever. U.S. Pat. No. 4,149,291 to Stoltz is an example of a brush having an elliptical motion which uses a crank-like configuration operating through a pivot to convert the rotation of a motor to the elliptical movement of the brushhead, while U.S. Pat. No. 3,978,852 to Annoni teaches a pivot arrangement in which the brush moves in a single plane.
All of these mechanically linked drive systems suffer from several disadvantages. Friction due to several surface-to-surface contact points in the various linkage arrangements produce significant power loss and result in rather low power efficiency for the various toothbrushes. While these disadvantages are not as significant when the toothbrush is powered from a 120-volt wall source, they do significantly limit the possibility of a battery-powered appliance capable of both scrubbing and acoustical cleaning. As a result, practical implementation of a battery-powered acoustic toothbrush has not occurred.
A magnetic drive system offers promise of relief from such power constraints. One of the significant advantages of a magnetic drive system is that the drive unit may be physically separate from the lever arm and hence the brushhead, which is at the far end thereof. Hence, any power loss due to mechanical linkages can be avoided. Examples of magnetically driven toothbrushes and/or similar appliances include U.S. Pat. No. 3,500,080 to Bey, which teaches a toothbrush driver comprising a combination of a permanent magnet and an electromagnet to drive a vibrating lever arm member and U.S. Pat. No. 2,734,139 to Murphy which teaches an electric eraser which includes an E core electromagnet having coils around the center leg thereof. Other patents which specifically teach a toothbrush using magnetic drive principles include U.S. Pat. No. 3,538,359 to Karl-Heinz Barowski, U.S. Pat. No. 2,977,614 to Demanuel, and U.S. Pat. No. 2,278,365 to Daniels. Further, Swiss patent No. 609238 specifically teaches a vibrating toothbrush which would appear to have an ultrasonic cleaning capability and which includes an ancillary magnetic drive system for indicating an excess load condition on the brushhead. The magnetic drive system includes a non-resonating arm and a limit on arm travel such that the system becomes non-operational at relatively small pressures.
Due to the overall design of such units, they are typically not very efficient and the use of battery power for such devices is not practical. A substantial amount of energy is usually lost in the form of air gap flux. Further the units are typically appropriate only for relatively low frequency vibration due to the high mass of the vibrating member and/or the drive system. Low frequency vibration makes fluid cavitation/streaming questionable for such units.
Hence, there remains a continuing need for an efficient, practical, power vibrating toothbrush which is capable of producing sufficient acoustical pressure to produce reliable cavitation and streaming as well as simultaneously scrubbing the teeth. It is desirable, furthermore, that the toothbrush be capable of operating from a battery. It is also desirable that the toothbrush vibrate with relatively minimal amplitude when unloaded, with an increase in amplitude when the bristles ar loaded. It is further desirable to minimize the number of moving parts in such a toothbrush, including avoiding mechanical linkages and complex sealing arrangements. It is still further desirable to prevent the user from applying force to the brush beyond a pre-established limit, in order to avoid excess abrasion and to allow bristles to vibrate in an acoustically effective manner.